1. Field of Invention
This invention relates to methods and apparatus for cardiopulmonary resuscitation and is particularly directed to improved methods and apparatus for performing direct heart massage.
2. Prior Art
In order to resuscitate a patient victim of a cardiac arrest, it is necessary to provide an adequate artificial circulation of oxygenated blood to the vital organs by reestablishing the pumping function of the heart at values as close as possible to the physiological prearrest condition. Such a cardiac pumping function must be instituted at the earliest possible stage. It is documented that a cardiac arrest results in irreversible brain death if a sufficient blood flow is not reestablished within a critical period of time from the moment of the cardiac arrest. Such a period of time is measured ranging between four and six minutes.
In order to reestablish the pumping function of the heart, two methods of cardiopulmonary resuscitation have been used heretofore: external or closed cardiac massage, and internal or open cardiac massage. Closed cardiac massage consists of applying pressure on the anterior chest wall and alternately releasing such pressure. In the vast majority of cases, closed chest compressions produce a severe low flow state (Raymond E. Jackson: Basic Cardiopulmonary Resuscitation. Emergency Medicine, American College of Emergency Physicians). Open chest cardiopulmonary resuscitation improves hemodynamics, resuscitation and the chance of surviving cardiac arrest. Cerebral blood flow achieved with open chest techniques has been shown to be near normal physiological values. There are several case reports of patients who have been resuscitated with direct cardiac massage when attempts with closed chest cardiopulmonary resuscitation have been unsuccessful (Advanced Cardiac Life Support Textbook, American Heart Association, page 42). However, few physicians today are skilled in the technique of direct cardiac massage. Since most cardiac arrests occur outside of a hospital and since most patients cannot be brought to a facility where a thoracotomy and direct cardiac massage can be performed in less that 15 minutes of total arrest time, the applicability of direct cardiac massage has been limited (ACLS textbook, page 42). In addition to that, this technique is often characterized by many physicians as a rather grossly traumatic procedure, often seen as a desperate terminal attempt to resuscitate an arrested heart.
The aforementioned drawbacks of the two prior art techniques of heart massage have been recognized by Prisk and Johnson, who proposed a new method and apparatus for which they obtained a patent (U.S. Pat. No. 3,496,932, issued Feb. 24, 1970). The method and apparatus described by Prisk and Johnson includes an inflatable bladder, insertable through the subxyphoideal region into a space between the sternum and the heart via a trocar-cannula assembly. In order to accommodate the inflatable bladder and its stem, the sharp three-sided tip of the trocar must have a comparably large diameter, as illustrated in FIG. 4 of the Prisk and Johnson patent. However, the larger the sharp three-sided trocar tip, the more likely are injuries to the heart, coronaries or surrounding organs. In addition to the risk inherent in the size of the sharp tip of the trocar, the blind advancement of a trocar with a sharp tip in the thoracic cavity has been proposed by Prisk and Johnson. Such blind advancement carries extremely high risk of puncturing and/or lacerating the heart, coronary vessels or the surrounding structures, with devastating consequences. Prisk and Johnson's proposed position of blindly inserting the trocar between the sternum and the pericardial sac is, indeed, an extremely risky procedure; this space being very narrow, while it is virtually impossible to insert the trocar into the other designated position, i.e. within the pericardial sac (This space being only virtual, since the visceral and parietal pericardium are in contact, separated only by a thin film of pericardial fluid). Furthermore, the device proposed by Prisk and Johnson lacks any mechanism for locating the position of the sharp tip of the trocar and lacks any safety mechanisms to prevent or avoid injuries, such as puncturing of the heart or coronary vessels. Moreover, an inflatable bladder with a laterally flexible stem, as proposed by Prisk and Johnson, lacks the required stability for maintaining its central position to effectively compress the heart. Also, the proposed inflatable-deflatable bladder has no guidance, thus lacking the ability to properly impress direction of the compressions toward the vertebral column, allowing the heart to be displaced during the phase of compression laterally to the column, and not maintaining the heart in position between the vertebral column and the sternum, as required for effective pumping and resulting in ineffective compression of the heart. Given the individual variability in the size and depth of the thoracic cage, the device of Prisk and Johnson is inadequate in that it has no means to adapt to the various depths of the thoracic cavity and ignores the variability in the distance between the sternum and the vertebral column. Finally, the method of insertion of the Prisk and Johnson bladder is a multistep manual procedure, which is necessarily time-consuming and conflicts with the need for a rapid institution of cardiopulmonary resuscitation. Thus, none of the prior art methods and apparatus for cardiac pulmonary resuscitation have been entirely satisfactory.